1. Technical Field
The present invention relates to a control apparatus which PWM (Pulse Width Modulation) controls an electromagnetic inductive load such as an electromagnetic clutch or a relay coil.
2. Background Art
Usually, an electromagnetic inductive load such as an electromagnetic clutch or a relay coil is subjected to the PWM control in order to reduce the power consumption. JP-A-2008-198850 shows one example of the above, and a current control apparatus disclosed therein is configured as shown in FIG. 24.
Referring to FIG. 24, a current which flows from a battery 1 to a clutch solenoid 3 that is a load, and a current sense resistor 4 through a transistor 2 is sensed via an amplification circuit 5, and, based on the sense value, a computing unit (microcomputer) 6 calculates a duty cycle so as to obtain a given average current amount as shown in FIG. 25, thereby PWM-driving the transistor 2.
In FIG. 24, reference numeral 7 denotes a freewheel diode, and reference numeral 8 denotes a clutch solenoid drive circuit. FIG. 25 shows graphs for illustrating a method of determining the duty cycle.